Injuries to soft tissue, such as cartilage, skin, muscle, bone, tendon and ligament, where the tissue has been injured or traumatized frequently require surgical intervention to repair the damage and facilitate healing. Such surgical repairs can include suturing or otherwise repairing the damaged tissue with known medical devices, augmenting the damaged tissue with other tissue, using an implant, a graft or any combination of these techniques.
One common tissue injury involves damage to cartilage, which is a non-vascular, resilient, flexible connective tissue. Cartilage typically acts as a “shock-absorber” at articulating joints, but some types of cartilage provide support to tubular structures, such as for example, the larynx, air passages, and the ears. In general, cartilage tissue is comprised of cartilage cells, known as chondrocytes, located in an extracellular matrix, which contains collagen, a structural scaffold, and aggrecan, a space-filling proteoglycan. Several types of cartilage can be found in the body, including hyaline cartilage, fibrocartilage and elastic cartilage. Hyaline cartilage can appear in the body as distinct pieces, or alternatively, this type of cartilage can be found fused to the articular ends of bones. Hyaline cartilage is generally found in the body as articular cartilage, costal cartilage, and temporary cartilage (i.e., cartilage that is ultimately converted to bone through the process of ossification). Fibrocartilage is a transitional tissue that is typically located between tendon and bone, bone and bone, and/or hyaline cartilage and hyaline cartilage. Elastic cartilage, which contains elastic fibers distributed throughout the extracellular matrix, is typically found in the epliglottis, the ears and the nose.
One common example of hyaline cartilage injury is a traumatic focal articular cartilage defect to the knee. A strong impact to the joint can result in the complete or partial removal of a cartilage fragment of various size and shape. Damaged articular cartilage can severely restrict joint function, cause debilitating pain and may result in long term chronic diseases such as osteoarthritis, which gradually destroys the cartilage and underlying bone of the joint. Injuries to the articular cartilage tissue will not heal spontaneously and require surgical intervention if symptomatic. The current modality of treatment consists of lavage, removal of partially or completely unattached tissue fragments. In addition, the surgeon will often use a variety of methods such as abrasion, drilling or microfractures, to induce bleeding into the cartilage defect and formation of a clot. It is believed that the cells coming from the marrow will form a scar-like tissue called fibrocartilage that can provide temporary relief to some symptoms. Unfortunately, the fibrocartilage tissue does not have the same mechanical properties as hyaline cartilage and degrades faster over time as a consequence of wear. Patients typically have to undergo repeated surgical procedures which can lead to the complete deterioration of the cartilage surface. More recently, experimental approaches involving the implantation of autologous chondrocytes have been used with increasing frequency. The process involves the harvest of a small biopsy of articular cartilage in a first surgical procedure, which is then transported to a laboratory specialized in cell culture for amplification. The tissue biopsy is treated with enzymes that will release the chondrocyte cells from the matrix, and the isolated cells will be grown for a period of 3 to 4 weeks using standard tissue culture techniques. Once the cell population has reached a target number, the cells are sent back to the surgeon for implantation during a second surgical procedure. This manual labor-intense process is extremely costly and time consuming. Although, the clinical data suggest long term benefit for the patient, the prohibitive cost of the procedure combined with the traumatic impact of two surgical procedures to the knee, has hampered adoption of this technique.
One common example of cartilage injury is damage to the menisci of a knee joint. There are two menisci of the knee joint, a medial and a lateral meniscus. Each meniscus is a biconcave, fibrocartilage tissue that is interposed between the femur and tibia of the leg. In addition to the menisci of the knee joint, meniscal cartilage can also be found in the acromioclavicular joint, i.e., the joint between the clavicle and the acromion of the scapula, in the sternoclavicular joint, i.e., the joint between the clavicle and the sternum, and in the temporomandibular joint, i.e., the joint of the lower jaw. The primary functions of meniscal cartilage are to bear loads, to absorb shock and to stabilize a joint. If not treated properly, an injury to the meniscus, such as a “bucket-handle tear” in the knee joint, may lead to the development of osteoarthritis. Current conventional treatment modalities for damaged meniscal cartilage include the removal and/or surgical repair of the damaged cartilage.
Another common form of tissue injury involves damage to the ligaments and/or tendons. Ligaments and tendons are cords or bands of fibrous tissue that contains soft collagenous tissue. Ligaments connect bone to bone, while tendons connect muscle to bone. Tendons are fibrous cords or bands of variable length that have considerable strength but are virtually devoid of elasticity. Ligaments, in contrast, are generally pliant and flexible, to allow the ligament tissue to have freedom of movement, and simultaneously strong and inextensible, to prevent the ligament tissue from readily yielding under applied force. Ligaments and tendons are comprised of fascicles, which contain the basic fibril of the ligament or tendon, as well as the cells that produce the ligament or tendon, known as fibroblasts. The fascicles of the tendon are generally comprised of very densely arranged collagenous fibers, parallel rows of elongated fibroblasts, and a proteoglycan matrix. The fascicles of ligaments also contain a proteoglycan matrix, fibroblasts and collagen fibrils, but the fibrils found in ligament tissue are generally less dense and less structured than the fibrils found in tendon tissue.
One example of a common ligament injury is a torn anterior cruciate ligament (ACL), which is one of four major ligaments of the knee. The primary function of the ACL is to constrain anterior translation, rotary laxity and hyperextension. The lack of an ACL causes instability of the knee joint and leads to degenerative changes in the knee such as osteoarthritis. The most common repair technique is to remove and discard the ruptured ACL and reconstruct a new ACL using autologous bone-patellar, tendon-bone or hamstring tendons. Although this technique has shown long-term clinical efficacy, there is morbidity associated with the harvest site of the tissue graft. Synthetic prosthetic devices have been clinically evaluated in the past with little long-term success. The advantages of a synthetic implant are that the patient does not suffer from the donor site morbidity that is associated with autograft procedures, and that patients having a synthetic implant are able to undergo faster rehabilitation of the knee. These synthetic devices were composed of non-resorbable materials and were designed to be permanent prosthetic implants. A number of problems were found during the clinical trials of these implants, such as for example, synovitis, bone tunnel enlargement, wear debris, and elongation and rupture of the devices. For this reason, autograft reconstruction is still the widely accepted solution for repairing a ruptured ACL.
A common tendon injury is a damaged or torn rotator cuff, which is the portion of the shoulder joint that facilitates circular motion of the humerus bone relative to the scapula. The most common injury associated with the rotator cuff is a strain or tear to the supraspinatus tendon. This tear can occur at the insertion site of the supraspinatus tendon, where the tendon attaches to the humerus, thereby partially or fully releasing the tendon (depending upon the severity of the injury) from the bone. Additionally, the strain or tear can occur within the tendon itself. Treatment for a strained tendon usually involves rest and reduced use of the tendon. However, depending upon the severity of the injury, a torn tendon may require surgical intervention, such as for example, in the case of a full tear of the supraspinatus tendon from the humerus. In the case of severe tendon damage, surgical intervention can involve the repair and/or reattachment of tom tissue, which typically requires a healing and recovery period.
There is a continuing need in this art for novel surgical techniques for the surgical treatment of damaged tissue (e.g., cartilage, meniscal cartilage, ligaments, tendons and skin) that can effect a more reliable tissue repair and can facilitate the healing of injured tissue. Various surgical implants are known and have been used in surgical procedures to help achieve these benefits. For example, it is known to use various devices and techniques for creating implants having isolated cells loaded onto a delivery vehicle. Such cell-seeded implants are used in an in vitro method of making and/or repairing cartilage by growing cartilaginous structures that consist of chondrocytes seeded onto biodegradable, biocompatible fibrous polymeric matrices. Such methods require the initial isolation of chondrocytes from cartilaginous tissue prior to the chondrocytes being seeded onto the polymeric matrices. Other techniques for repairing damaged tissue employ implants having stem or progenitor cells that are used to produce the desired tissue. For example, it is known to use stem or progenitor cells, such as the cells within fatty tissue, muscle, or bone marrow, to regenerate bone and/or cartilage in a patient. The stem cells are removed from the patient and placed in an environment favorable to cartilage formation, thereby inducing the fatty tissue cells to proliferate and to create a different type of cell, such as for example, cartilage cells.
There continues to exist a need in this art for novel devices and methods for making and/or repairing damaged tissue and for hastening the healing of the damaged tissue.